Republicans have run three times as many ads focused on tax reform as Democrats have so far this year, and the battle is just beginning. An exclusive USA TODAY analysis shows the pivotal role of tax cuts in political advertising.

WASHINGTON — Republicans are pinning their midterm election hopes on the massive tax overhaulsigned into law last year, and it shows.

GOP groups and candidates have run nearly 17,800 spots this year that tout tax reform, according to a USA TODAY analysis of television advertising. The barrage has forced Democrats to retaliate with commercials that slam the tax cuts as helping the wealthy -- and endangering Medicare and Social Security in the years ahead.

Americans for Prosperity, a deep-pocketed group aligned with conservative billionaire Charles Koch, is helping to drive the Republican spending as it pummels vulnerable Democratic senators in states friendly to President Trump.

The group boughtmore than a third of the television spots mentioning the tax overhaul passed by the Republican-controlled Congress in December, according to data provided by Kantar Media’s Campaign Media Analysis Group (CMAG), which tracks political advertising.

The analysis also finds that overall, advertising on the broader topic of taxes is soaring. On local broadcast stations, nearly 27,000 ads focused on congressional races mentioned taxes between Jan. 1 and April 9. That accounts for 32% of all advertising targeting House and Senate contests, up from 13% at the same point in 2016 and 16% in 2014, the most recent midterm elections.

With tax returns for 2017, the last year for the old tax code, due on Tuesday, consultants and campaign officials say the heaviest spending on ads to highlight the new codeis just starting.

"Every Republican member of Congress needs to run on the middle-class tax cut and win on the middle-class tax cut," said Corry Bliss, who oversees the Congressional Leadership Fund, a super PAC aligned with House Republicans and its nonprofit arm, the American Action Network.

The groups have spent $7 million promoting the tax cuts since the start of the year and on Monday announced another $1 million round of national television and digital advertising.

"This election sets up a central contrast: One party cut your taxes. The other party mocked you and your tax cut," Bliss said. "If you are living paycheck to paycheck, and someone gets you an extra $2,000 next year, that's a big deal."

Democrats fight back

But the tax law, which made a 40% reduction in the top corporate tax rate permanent while setting a 2025 expiration date on cuts to individual taxes and rates, affects taxpayers differently based on where they live, the kind of work they do, how many children they have and what year the impact is being measured.

Not One Penny has already run nearly 1,550 ads in Arizona, Iowa and Nevada aimed at vulnerable Republican incumbents, and spokesman Tim Hogan said the group plans to spend $5 million this year. Pelosi and Senate Democratic leader Chuck Schumer will headline a rally Tuesday assailing the tax overhaul on Capitol Hill.

Republicans face stiff headwinds in this year's elections. Trump's approval ratings remain below 50% in most recent polls, and a first-term president’s party typically loses ground in Congress in midterm elections. House Speaker Paul Ryan, R-Wis., announced his retirement Wednesday, dealing another blow to Republicans' fight to retain their 23-seat majority in the House.

The GOP sees taxes as “a lifeline in a very bleak political environment,” said Democratic pollster Geoff Garin. “The only virtue of this issue for Republicans is that every other issue is worse.”

Republicans' prospects in the Senate are far better. They are defending just nine seats, while Democrats are defending 26, including 10 in states where voters backed Trump in 2016.

Early advertising on the tax bill by Americans for Prosperity has targeted Indiana, Missouri and North Dakota, where Democratic Sens. Joe Donnelly, Claire McCaskill and Heidi Heitkamp are seeking reelection in states Trump captured by large margins.

The AFP advertising is part of a $20 million campaign by Koch-aligned groups to sell the tax overhaul to voters. That's prompted Democratic groups, such as the Senate Majority PAC, to go up on the air early to play defense.

Polls are divided

For a law that supporters say is putting $2,000 in the pockets of middle class families, the tax plan appears to need some selling.

National polls by Quinnipiac University show approval of the tax plan grew from 26% to 39% between mid-December and early February, then dropped to 36% in early March. Disapproval, which was at 55% in mid-December, was at 50% in early March.

A Monmouth University poll released March 7 found adults were divided on the law, with 41% approving and 42% disapproving. But while the number of adults who believed their taxes would go down grew from the 14% measured in December, it only reached 23% in March.

"We think it's a process to make sure Americans know about" the tax cuts, said AFP President Tim Phillips. "There's a lot of skepticism about what comes out of Washington from both parties. But on tax cuts and tax reform, it's a good policy that's helping the vast majority of Americans."

It is also an open question whether focusing on the tax law will help the GOP, given the results of a recent special election in southwest Pennsylvania. Democrat Conor Lamb was sworn into Congress on Thursday, having survived an onslaught of nearly 1,350 tax-related ads from Republicans to win a narrow victory in a district that Trump carried by nearly 20 percentage points in 2016.

Lamb responded with his own ad, saying he supported a middle class tax cut but not the bill Trump signed in December.

“Of course, they never mention their tax plan increases the deficit by $1.5 trillion,” Lamb’s ad, which aired 153 times on Pittsburgh-area stations, said. “Or that many Pennsylvanians will have their tax cut wiped out by higher health care premiums. Or that their next step is to cut Medicare and Social Security."

"Republicans win on this if they are unchallenged," he said. "But when we make both arguments, we're confident that we are going to win on the issue."

Republicans have said Lamb's win was driven more by an opponent who ran a weak campaign than any messages on the airwaves. Kantar's data shows Senate Majority lagging behind AFP, running about half as many spots as the Koch-aligned group.

"In this space, the Koch brothers seems to have unlimited money, but we're doing our best to compete with them everywhere we can," Hayden said.

Jennifer Duffy, an analyst at the Cook Political Report, which handicaps congressional races, said the battle over taxes will be most heated in states Trump carried where Democrats are trying to be re-elected.

"Voting against tax reform means voting against Trump," Duffy said. “For the Donnellys and the McCaskills, who claim to be moderates who vote with their constituents, this is something that Republicans believe is evidence they do not."